A 'tool-less' wooden option (if
VA-gunnut's option is not appealing) would be to go to your local lumber yard (maybe even Home-Depot/Lowes) and buy sufficient dimensional lumber to meet your goals. They'll generally cut to-length lumber you purchase there, perhaps for a small fee. For example, buying three pieces of 4" x 4" x 8' (fir ... or if you're rich, a harder wood, like oak
) would allow you to put together a pedestal that is nominally 4" x 24" x 4'. The actual size would be closer to 3 1/2" x 22" x 47".
If you opt for the brick/wood solution, wrap the room-facing, outer surface of the sticks/bricks with duct tape prior to the installation. This will keep the ad-hoc pedestal together/in place during the installation; the tape can be removed after the safe's in place.
Should you choose wood, a staple gun and razor-knife would allow you to easily cover your pedestal with carpet of your choice; it'll look 'professional' thanks to the carpet. Select a carpet with dense backing and smear everything with lots'a glue before you staple the carpet down. (I'd avoid using pressure-treated stock ... unless your safe is going to be installed in a garage or outbuilding.)
(I've intentionally stayed away from the issues related to attaching the safe firmly to your building, which generally takes place through holes in the safe's base.)